Subpoena rules vary state by state. While there are some states that have adopted the Uniform Interstate Depositions and Discovery Act, many others have not. It can become very complex very quickly when having to deal with interpreting conflicting deadlines and procedures between the two states. Therefore, I strongly recommend you consult an attorney for a case evaluation. It may cost you for their expertise, but it should be well worth it in the end when you have a successful result.
Typically you have to get a court in your state issue a commission to take an out of state deposition. Which them is filed in the other state court for issuance of a subpoena to obtain jurisdiction over the person. These actions can be complex. Consult an attorney for more guidance .
DISCLAIMER: Brandy A. Peeples is licensed to practice law in the State of Maryland. This answer is being provided for informational purposes only and the laws of your jurisdiction may differ. This answer based on general legal principles and is not intended for the purpose of providing specific legal advice or opinions. Under no circumstances does this answer constitute the establishment of an attorney-client relationship. For legal advice relating to your specific situation, I strongly urge you to consult with an attorney in your area. NO COMMUNICATIONS WITH ME ARE TO BE CONSTRUED AS ARISING FROM AN ATTORNEY-CLIENT RELATIONSHIP AND NO ATTORNEY-CLIENT RELATIONSHIP WILL BE ESTABLISHED WITH ME UNLESS I HAVE EXPRESSLY AGREED TO UNDERTAKE YOUR REPRESENTATION, WHICH INCLUDES THE EXECUTION OF A WRITTEN AGREEMENT OF RETAINER.
My colleagues are generally correct insofar as you probably need an attorney to take the helm on something involving multistate or multi-jurisdiction litigation. To give you an idea of how complicated of a process it is to subpoena the deposition of a nonresident, take a look at Rule 4:14-7 of the New Jersey Court Rules. Also, keep in mind that you will have to hire a process server to serve the subpoena, and you must must tender to them statutory mileage/witness fees upon service. You also need to hire a court reporter to take the deposition. None of this will be easy to accomplish pro se.
Here's a question for you: Is your wife represented by counsel in this case? If so, that's a clear sign that you have to retain counsel as well. It's one thing to go to court pro se, when the other side is also unrepresented, but only bad things can happen to you when you try to face off with someone with legal training, regardless of their skill level.
I am admitted to practice in the states of New Jersey and Ohio. Regardless of where you are reading this, my comments are not intended to be legal advice per se, and nothing that I say is intended to create an attorney–client relationship.